The present invention relates to encoded symbol readers used to decode encoded symbols such as two dimensional tessellated codes.
Modern point-of-sale systems employ encoded symbol readers to scan product bar-code labels, thereby increasing processing speed at store check-outs. However, conventional bar-code labels are scanned in only one dimension (i.e., a single scanning direction), and the bar-codes can only encode a small amount of data. More recently, a new type of symbol for representing data in two directions has been proposed. This new type of symbol (hereinafter referred to as a tessellated code) uses a two-dimensional tessellated pattern to represent data.
A relatively simple scanning process is employed for conventional (single-direction) bar-codes, in which the angle between the reference surface on which the bar code is printed and the encoded symbol reader is not critical. Similarly, the distance between the printed bar-code and the light receptor of the encoded symbol reader is not critical.
If a simple scanning method is used to read tessellated codes, the positioning of the encoded symbol reader is crucial for decoding the appropriate information. If the surface bearing the tessellated code and the image receiving element are not aligned properly, the received image may be distorted and the wrong information decoded. Furthermore, the distance from the tessellated code to the light receptor of the encoded symbol reader is best kept constant to properly decode the tessellated code. Positioning the encoded symbol reader is difficult if the tessellated code is not printed on a surface that is both flat and in a level position.
An area sensor has been developed for the encoded symbol reader in order to read the two-dimensional symbols. The area sensor scans the entire tessellated pattern simultaneously, in essence taking a "snapshot" of the encoded symbol. Alternatively, a line sensor may be used, where each line of encoded dots of the tessellated code is main scanned along the line, and auxiliary scanned from line to line. However, either type of encoded symbol reader must be positioned at a specific distance and angle (within certain tolerances) with respect to the tessellated code. An example of a known encoded symbol reader employing this type of area sensor is shown in FIG. 1.
FIG. 1 shows an encoded symbol reader 100 including a main body 101 and a reading head 103. The reading head 103 houses a reading module 102. FIG. 2 shows a top view of an window 104 formed in the reading head 103. The window 104 is a physical space defined by the walls 105. A reading field 36 is defined within the window 104, delineating an area in which the encoded symbol may be read. The reading field 36 is a virtual space defined by the field of view sensable by the reading module 102.
As shown in FIG. 2, part of the encoded symbol 38 maybe covered by the rectangular wall 105, but still inside the outer peripheral surface 106 of the reading head 103. The user may thus assume that the entire symbol 38 is readable by the reader 100, yet proper decoding of the symbol 38 is not possible. Further, even if the rectangular wall 105 is a translucent material, it is still difficult to ensure that the symbol 38 is within the reading field 36.